In recent years, the importance of coating technology has been rapidly rising. Various coating methods have been developed.
However, no coating method able to form a high density coating film of a thickness of several tens to several hundreds of micrometers has been known.
The document (A. Yumoto, F. Hiroki, I. Shioda, N. Niwa, Surface and Coatings Technology, 169-170, 2003, 499-503) and the document (Atsushi Yumoto, Fujio Hiroki, Ichiro Shiota, Naotake Niwa: Formation of Ti and Al Films by Supersonic Free Jet PVD, Japan Metal Society Journal, Vol. 65, No. 7 (2001), pp. 635-643) disclose a supersonic free jet (SFJ)-physical vapor deposition (PVD) system.
This SFJ-PVD system is provided with an evaporation chamber and a film formation chamber.
The evaporation chamber is provided with an evaporation source material disposed on a water cooled hearth and an electrode made of a high melting point metal (specifically tungsten). The interior of the evaporation chamber is reduced once to a predetermined pressure, then the atmosphere changed to a predetermined gas, then the evaporation source is used as an anode an electrode made of a high conductivity metal located at a position a certain distance away from the anode is used as a cathode, and a negative voltage and a positive voltage are applied to them to induce an arc discharge between the two poles, that is, transfer type arc plasma is used, to heat and evaporate the evaporation source material. In the evaporation chamber rendered to the predetermined gas atmosphere, atoms evaporated due to the heating of the evaporation source agglomerate with each other whereby microparticles having diameters of the nanometer order (hereinafter referred to as “nano particles”) are obtained.
The obtained nano particles ride the flow of gas induced by a pressure difference (vacuum degree difference) between the evaporation chamber and the film formation chamber pass through a transfer pipe and be transferred to the film formation chamber. In the film formation chamber, a substrate for film formation is disposed.
The flow of gas due to the pressure difference is accelerated to the supersonic speed of about Mach 3.6 by a specially designed supersonic nozzle (Laval nozzle) attached to a front end of the transfer pipe connecting the evaporation chamber to the film formation chamber. The nano particles ride on the stream of the supersonic free jet, are accelerated to a high speed, and are ejected into the film formation chamber and deposited on the substrate for film formation.
By using the above SFJ-PVD system, it becomes possible to form a high density coating film having a thickness of several tens to several hundreds of micrometers at a low temperature.
Plasma torches can be roughly classified into the transfer type and the non-transfer type.
FIG. 1A and FIG. 1B are schematic views of the configurations of plasma torches of the transfer type and the non-transfer type according to the prior art.
As shown in FIG. 1A, a transfer type plasma torch is comprised of a substantially cylindrical plasma tip 1 at the center of the inner side of which a rod shaped internal electrode 3 acting as the cathode is inserted. By applying a positive voltage to a heated object S and a negative voltage to the internal electrode 3, arc plasma is induced due to the discharge between the heated object S and the internal electrode 3 and thereby the heated object 3 is heated.
On the other hand, as shown in FIG. 1B, a non-transfer type plasma torch is comprised of a substantially cylindrical plasma tip 1 at the center inside which an internal electrode 3 is inserted. The plasma tip 1 is used as the anode and the internal electrode 3 is used as the cathode to induce an arc discharge between the poles. Plasma gas G is supplied between the poles. The heated object S is heated using the plasmatized gas as a medium.
A transfer type plasma torch has the advantage that the energy efficiency is high since current flows to the heated object to generate Joule's heat, but needs an electrode for generating the plasma and holding the plasma until the heated object melts and becomes conductive, so is not suitable for heating and melting an insulator. Further, to hold the arc voltage constant at the time of arc discharge, it is necessary to keep the distance between the two poles in constant. However, the anode side constituted by the heated object changes in its shape and volume successively due to melting and evaporation, therefore it is not easy to precisely control the amount of evaporation from the heated object.
On the other hand, a non-transfer type plasma torch has the advantages that it can generate plasma without being influenced by the material of the heated object since current does not flow to the heated object and that a starting property and stability of the plasma are high and controllability of the amount of heating is better in comparison with heating by a transfer type plasma torch.
Note that a non-transfer type plasma torch has two electrodes of the anode (plasma tip) and the cathode (internal electrode) in the torch. They must be insulated from each other. For this reason, in a conventional non-transfer type plasma torch, BAKELITE® phenol resin, or another polymer based insulating material is used in order to secure insulation between the two electrodes.
Because of the above polymer-based insulating material and other torch materials, when using the conventional non-transfer type plasma torch in an ultra-high vacuum environment, outgas ends up being generated.
For this reason, in a SFJ-PVD system, when using the plasma generated in a plasma torch to generate nano particles from an evaporation source, the obtained nano particles end up being polluted by the outgas.
Further, when there are a plurality of evaporation chambers, it is necessary to uniformly mix for example first microparticles and second microparticles. In this case, a first fluid including the first microparticles and a second fluid including the second microparticles are mixed.
For example, the Y-shaped fluid mixing device shown in FIG. 2 may be used to mix the above first and second fluids.
The Y-shaped fluid mixing device is comprised of a first inflow port 101 into which a first fluid 100 flows and a second inflow port 111 into which a second fluid 110 flows merging for mixture at a merging part 120, a mixture of the first fluid 100 and the second fluid 110 being taken out of a takeout port 130.
In the above Y-shaped mixing device, even when making the first fluid and the second fluid simultaneously flow in, due to the viscosities etc. of the fluids, sometimes they will not be mixed at the merging part, but will end up being discharged from the takeout port while substantially separated. Uniform mixture is sometimes difficult.
Here, for more uniform mixing of the first fluid and the second fluid, electrical energy from the outside is used to the mechanically control the inflows of the first fluid and the second fluid to the takeout port. More specifically, as shown in FIG. 2, the first fluid and the second fluid are controlled so as to alternately flow to the takeout port. By making the amounts of fluids alternately flowing in smaller, it becomes possible to more uniformly mix the first fluid and the second fluid.
Therefore, for mixing the first fluid and the second fluid as described above, a method of mixing fluids such as the conventional Y-shaped mixing device not requiring electricity or other energy from the outside and not providing mechanical moving parts is demanded.